Australopithecus afarensis had a very low forehead,
a face that projected far forward (as viewed in profile), and a very prominent
brow ridge. A. afarensis is the earliest species for which we have
reliable brain and body size estimates, thanks to a rich fossil record for
the species.

The brain of A. afarensis was about one-third the size of
the average modern human brain, or about the same size as a modern ape's brain.
Males and females varied significantly in body size, with males standing
approximately 4 feet 11 inches tall and weighing 100 pounds and females standing
about 3 feet 5 inches tall and weighing about 62 pounds. Males also typically
had large crests on top of their skulls; females did not.

The knee and pelvic
bone structure of A. afarensis were very humanlike, leaving no doubt that
A. afarensis walked upright. A. afarensis probably inhabited the
savannas and open woodlands where they likely found fruits, seeds, and roots.

These fossilized footprints reveal important information
about the two individuals who made them. First, it's clear that they walked
upright. Also, from stride length, scientists estimate that they were about
4 feet 8 inches and 4 feet tall, respectively. (The footprints are linked
to A. afarensis by the fossil jawbones of the same species found
nearby.)

This intact A. afarensis knee joint looks very much
like a small version of an anatomically modern human knee and likely worked
similarly. The angle of the joint all but confirms A. afarensis's
ability to walk upright.